The present invention relates to a timing variator between the crankshaft and the camshaft of an internal combustion engine.
As is well known, the timing variator of an internal combustion engine is a mechanism which enables the timing system setting to be changed to optimize the engine performance at varying loads and rpm.
A timing variator commonly employed is a hydromechanical type having a first element connected drivingly to the engine crankshaft, a second element connected drivingly to the timing system camshaft, and a piston member mounted between and coupled to said elements. In particular, the piston member is coupled to one of the two elements by means of helical gears. The piston member is moved relative to said elements by a working fluid which is regulated by a valve under control by an electronic control unit for the engine. The movement of the piston member produces, through the gear coupling arrangement, a relative angular displacement of said two elements, thereby changing the timing angle relationship of the camshaft to the crankshaft, and hence the engine valve timing.
However, timing variators of the type outlined above may present a problem of substantial importance.
In conjunction with the classic timing system including valves and valve springs, due to continued reversal of the reaction load on the camshaft, as produced by the timing system dynamic mode during the variator operation, rattling noise is generated by a continued mutual reciprocation of the enmeshed teeth as the load direction is reversed which is due to their backlash. This makes for noisy operation of the timing variator and the engine to which it is incorporated. In addition, the gear teeth rate of wear is increased.
To avoid this problem, a perfect fit would have to be provided between the teeth of the coupling arrangements, but this is quite difficult to accomplish in the manufacturing process, and hence impractical.
Solutions to the problem have actually been proposed. One solution provides a split piston member in two parts to effectively offset consecutive helical gear sections on the two parts by application to such parts of an appropriate elastic load to take up the backlash between the teeth. Another solution provides for the fast reciprocating movements of the gears to be damped by a viscous fluid. Such solutions involve, however, significant structural and functional complications that lead to high manufacturing costs and inferior reliability.